The present invention relates to systems for purging containers, and more particularly relates to a container flush and gas charge system and method for evacuating corrosive or contaminating moisture, air, particles or gases from an article container such as a semiconductor wafer pod and charging the container with a fresh supply of inert gas.
A standardized mechanical interface (SMIF) system is disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. Such a SMIF system is designed to reduce particle fluxes onto semiconductor wafers and/or reticles in a semiconductor production facility. The SMIF system prevents or minimizes particle contamination of the wafers during transport and storage of the wafers by ensuring that gaseous media surrounding the wafers is essentially stationary relative to the wafers, and further, by preventing exposure of the wafers to particles from the ambient environment.
The SMIF concept is based on the use of a small volume of motion- and contamination-controlled, particle-free gas to provide a clean environment for semiconductor wafers and other articles. Further details of one such system are described in a paper entitled, xe2x80x9cSMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURINGxe2x80x9d, by Mihir Parikh and Ulrich Kaempf, Solid State Technology, July 1984, pp. 111-115.
SMIF systems are designed to prevent contamination by particles which range from below 0.02 xcexcm to above 200 xcexcm. Due to the small geometries of the components in modern semiconductor integrated circuits, particles falling within this size range can significantly adversely affect semiconductor processing. Current geometry sizes for semiconductor integrated circuits have reached less than half a micron, and those circuits are adversely affected by particles having a size as small as 0.01 xcexcm. In the future, semiconductor integrated circuits will be marked by increasingly smaller geometry sizes, requiring protection from contamination by correspondingly smaller particles.
In a typical SMIF system, semiconductor wafers are stored and transported in wafer cassette containers, or pods, and are transferred from the pod to processing equipment typically in the following manner. First, the pod is placed at the interface port of a processing tool. Each pod includes a box and a box door designed to mate with doors on the interface ports of the processing equipment enclosures. Then, latches release the box door, and the box door and the interface port door are opened simultaneously such that particles which may have adhered to the external door surfaces are trapped or sandwiches between the box and interface port doors. A mechanical elevator lowers or translates the two doors, with the cassette riding on top, into the enclosure-covered space. The cassette is transferred by gravity or a manipulator and placed onto the cassette platform of the equipment. After processing, the reverse operation takes place.
FIG. 1 illustrates a load port configuration which utilizes a SMIF 10 such as an indexer to transfer a wafer cassette 22 carrying multiple semiconductor wafers 24 from a SMIF pod 16 to a process tool (not illustrated), such as an etcher, for example, and from the process tool back to the SMIF pod 16. In this type of load port configuration, the SMIF pod 16 is first loaded onto the load port 11 of the indexer 10, typically from an overhead transport vehicle (OHT) or automatic guided vehicle (AGV), with the bottom pod door 20 of the SMIF pod 16 initially attached to the shell 18 thereof and resting on the port door 12 of the load port 11. As the port door 12 is lowered into the SMIF 10, the shell 18 of the SMIF pod 16 remains at the load height (typically 900 mm) at the level of the port plate 14 of the load port 11. Simultaneously, the pod door 20 resting on the port door 12 is uncoupled from the shell 18 and the cassette 22 containing the wafers 24 is lowered with the supporting port door 12 into a minienvironment beneath the SMIF 10. From the minienvironment, the cassette 22 and/or wafers 24 are transferred to and from the process tool for processing of the wafers 24. After wafer processing, the cassette 22 holding the processed wafers 24 is transferred back to the port door 12 of the SMIF 10, and the port door 12 is raised and lifts the cassette 22 back into the shell 18 and replaces the pod door 20 on the shell 18. The re-assembled SMIF pod 16 is then removed and transported either manually or by an OHT or AGV to another location for further processing.
One of the problems frequently encountered in operation of the SMIF load port configuration 10 is that residual corrosive process gases from the process tool tend to become recaptured in the shell 18 of the SMIF pod 16 when the pod door 20 is raised back in place on the shell 18 by the port door 12. This tendency is particularly problematic in ballroom-type cleanrooms in which an inert gas is not discharged into the SMIF pod 16 after wafer processing to dispel the residual process gases in the SMIF pod 16. Exposure of the encapsulated wafers 24 to corrosive gases in the SMIF pod 16 during subsequent transfer to the next processing tool tends to induce corrosion and contamination of the wafers, as well as shorten wafer Q-time and adversely affect wafer yield performance.
Accordingly, an object of the present invention is to provide a system for controlling the interior environment of an article-carrying container to prevent corrosion of articles in the container.
Another object of the present invention is to provide a system which is capable of purging corrosive gases from an article-carrying container in a manufacturing or other facility.
Another object of the present invention is to provide a system which is capable of restoring an inert gas to a semiconductor wafer pod to prevent or reduce the incidence of corrosion or contamination of semiconductor wafers stored or transported in the pod.
Still another object of the present invention is to provide a system which is capable of evacuating corrosive gases and potential contaminants from a wafer cassette container or pod and restoring a desired gaseous environment inside the wafer cassette container or pod.
Yet another object of the present invention is to provide a method for the purging of potential corrosive residual process gases from a semiconductor wafer pod interior and restoring a normal clean, inert gaseous environment inside the pod to minimize yield contamination and corrosion of semiconductor wafers transferred in a semiconductor production facility.
In accordance with these and other objects and advantages, the present invention comprises a system and method for evacuating potential wafer-corroding and contaminating residual process gases from the interior of a semiconductor wafer pod before, after or both before and after a process is performed on the wafers. The residual process gases are first evacuated from the wafer pod, which is next charged with a fresh supply of inert gas. The system is adapted to evacuate and charge the wafer pod as the wafer pod typically rests on a load port of a SMIF prior to transfer of the pod to another destination in the semiconductor fabrication facility, prior to internalization of the wafers into a processing tool, or both.
According to a typical embodiment of the present invention, a vacuum/exhaust line communicates with the pod interior to remove residual process gas from the pod interior as the pod contains a wafer-filled cassette and rests typically on a load port of a SMIF before internalization of the wafers or wafer-filled cassette into a processing tool such as an etcher, for example, or transfer of the wafer-filled pod from the SMIF to a processing tool or other destination in the clean room or facility. An inert gas supply line communicates with the pod interior and extends from an inert gas source for introducing a fresh supply of inert gas into the pod after the evacuation step. The system can be operated to evacuate the pod and charge the pod with a fresh supply of inert gas before, after, or both before and after the process is performed on the wafer.
According to a typical embodiment of the present invention, the removable bottom door of the pod is modified to establish fluid communication between the pod interior and the gas supply line and the vacuum/exhaust line, respectively, of the system. The pod door and the inert gas supply line and vacuum/exhaust line may each be provided with quick connect/disconnect couplings to facilitate quick and easy, removable attachment of the pod to the gas supply line and the vacuum/exhaust line, respectively. The gas supply line and vacuum/exhaust line may extend through an elevatable port door on the SMIF, wherein one set of the quick connect/disconnect couplings are located on the port door and the other set of companion quick connect/disconnect couplings are provided on the pod door. Accordingly, the interior of the wafer pod is disposed in fluid communication with the gas supply line and the vacuum/exhaust line when the wafer pod is supported on the port door of the SMIF.
A pair of valves may be provided in the gas supply line and the vacuum/exhaust line, respectively, for controlling flow of inert gas through the gas supply line and establishing or dissipating vacuum pressure in the vacuum/exhaust line, respectively. An interface circuit may be provided in the system for receiving a signal from the SMIF controller and facilitating implementation of the evacuating step and the gas charging step, respectively, by controlling the valves, prior to removal of the wafer cassette from the pod, after replacement of the wafer cassette in the pod, or both.